This invention relates to oil supply systems for supplying lubricating and/or cooling oil to machines such as internal combustion engines.
In German Offenlegungsschrift No. 3 711 792, an oil supply for an internal combustion engine has an oil delivery line which descends from an elevated oil reservoir to the engine parts such as bearings that are to be supplied with oil. In order to transfer the entire amount of oil necessary for lubrication or cooling of the engine from the oil pan through an ascending line into the elevated oil reservoir, the ascending line is designed so that a sufficiently high pressure in the area of the oil pan will assure the required transfer. This arrangement has the fundamental advantage that it eliminates the need for an oil pump for conveying the oil from the oil pan into the oil reservoir and a very small volume of oil can be maintained in the oil pan because of the presence of the oil reservoir within or on the side of the engine. Therefore, the oil level in the oil pan can be very shallow, but this presupposes that the proper pressure conditions are established and thus that the oil pan has a virtually airtight seal with respect to the atmosphere. As a rule, however, the oil pan communicates with bearings for moving parts, such as crankshaft bearings, which are not airtight and which are exposed to atmospheric pressure on the other side. Furthermore, it is often of interest to be able to monitor the oil level in the oil pan with a dipstick. The opening for such a dipstick permits leakage of pressure from the oil pan.
A device for automatically replenishing the oil in the crankcase of an internal combustion engine is disclosed in German Patent No. 2 940 235, wherein an oil delivery line and an oil pump are connected to the intake side of the oil volume in the oil pan and an elevated refill tank that is sealed with respect to the atmosphere resupplies used oil to the oil pan through a valve arrangement. However, no arrangement for transporting oil to the refill tank is provided in this device, nor does that patent disclose any arrangement for avoiding the use of an additional pump by utilizing certain pressure conditions in the refill tank and the oil pan area.